Thermoelectric Performance Of Ag-In-Se(Te) Ternary Chalcogenides

In this work,AgInTe₂,AgInSe₂ and Ag₃In₅Se₉ semiconductor materials were prepared by using powder metallurgy technology,along with the spark plasma sintering（SPS）.AgInTe₂ compound has not received enough recognition in thermoelectrics,possibly due to the fact that the presence of many kinds of defects,such as,Te vacancy(V_Te)and antisite defect of In at Ag site(In _Ag),degrades its electrical conductivity.In this work,we prepared the Ag_1-xInTe₂ compounds with substoichiometric amounts of Ag and observed an ultralow lattice thermal conductivity(κ_L=0.1 Wm^-1K^-1)for the sample at x=0.15 and 814 K.This leads to more than 2-fold enhancement in the ZT value（ZT=0.62）compared to the pristine AgInTe₂.In addition,we have traced the origin of the untralowκ_L using the Callaway model.The results attained in this work suggest that the engineering of the silver vacancy concentration(V_Ag)is still an effective way to manipulate the thermoelectric performance of AgInTe₂,realized by the increased point defects and modified crystal structure distortion as the V_Agg concentration increases.Similarly,the AgInSe₂ semiconductor compound has not received enough recognition either in thermoelectrics.Because it has a wider band gap,it is easy to engineer its band structure through doping,which optimizes its carrier concentration and improves the electrical conductivity.In addition to,an introduction of multiphase structure may increase the scatterings on the grain boundaries and point defects,thus realizing the reduction in lattice thermal conductivity.Guided by this thinking,（AgInSe₂）（Ag₂Se）_x samples were prepared by doping Ag₂Se.It was found that with an increase of Ag₂Se the grain boundary scattering enhances,thus the lattice thermal conductivity(κ_L=0.15 Wm^-1k^-1,x=0.3,T=845 K)further reduces.As a consequence,thermoelectric figure of the merit（ZT）for the final material increases to 0.88（x=0.3）,about 2.7 times that of intrinsic AgInSe₂.In order to improve the thermoelectric properties of Ag₃In₅Se₉,we specially substituted Cu on Ag in this compound,that is,Ag_3-xCu_x In₅Se₉.The results revealed that the ZT value increased from 0.3（x=0）to 0.46（x=1）,indicating that the isoelectronic element substitution was still an effective way to improve the thermoelectric performance.